A telephone instrument usually includes a microphone which functions as a transmitter and an earphone which functions as a receiver. The transmitter and the receiver are coupled to a telephone line by an interface. In an analog telephone set, for example, the interface performs a hybrid function which includes directing signals from the transmitter to the telephone line and directing signals from the telephone line to the receiver.
A telephone operator or attendant may use a headset which includes a microphone and a single earphone or a pair of earphones for left and right ears. At present, there is little advantage to using a pair of earphones as the signals on the telephone line lack binaural information. Hence, the telephone user must listen to sounds which lack the quality of sound in a normal listening environment.
U.S. Pat. No. 4,694,497 granted to Junichi Kasai et al on Sep. 15, 1987 and U.S. Pat. No. 4,953,219 granted to Junichi Kasai et al on Aug. 28, 1990 disclose reproduction of stereophonic sound signals adapted to multiple speakers from a stereo sound signal. This, however, is not applicable to reproduction of sounds characteristic of a normal listening environment from monaural sound signals.
U.S. Pat. No. 4,338,581 granted to Nelson H. Morgan on Jul. 6, 1982 discloses room sound simulation. M. R. Schroeder teaches artificial reverberation in the Journal of the Audio Engineering Society, Vol.10, Number 3, pp. 219-223 (July 1962). Neither, however, suggests reproduction of sounds characteristic of a normal listening environment from monaural sound signals.